1. Field of the Invention
The invention relates to an overvoltage protector with a housing and with at least one overvoltage limiter which is located in the housing, the overvoltage limiter being especially a gas-filled surge arrester, a spark gap, a suppressor diode or a varistor.
2. Description of Related Art
Overvoltage protection can be divided into different areas of application. Here, it is distinguished between overvoltage protection for power supply, for measurement, open-loop and closed loop control (MSR) technology and for information technology and telecommunications. Interfaces of MSR technology are far more sensitive to overvoltages than power supply systems. For overvoltage protection, therefore, in the MSR domain, generally, overvoltage protectors with combined protective circuits are used, at least one overvoltage limiter being used for coarse protection and at least one overvoltage limiter being used for precision protection. Often, an indirect parallel connection of a gas-filled surge arrester and a suppressor diode is used, a decoupling resistor being located between the gas-filled surge arrester and the suppressor diode.
The known overvoltage protectors are often made as “protective plugs” which form an overvoltage protection device together with the bottom part of the device. For installation of this overvoltage protection device, there are corresponding terminals for the individual conductors on the bottom part of the device. For simple mechanical and electrical contact-making of the bottom part of the device with the respective overvoltage protector, the connecting elements in the overvoltage protector are made as plug pins for which there are corresponding sockets connected to the terminals in the bottom part of the device so that the overvoltage protector can simply be slipped onto the lower part of the device.
In these overvoltage protection devices, the installation and mounting can be done very easily in a time-saving manner due to the plug-in capacity of the overvoltage protector. In addition, these overvoltage protectors partially have a remote reporting capability, as a primary detector of the state of the overvoltage protector which is conventionally made as a changeover contact, and an optical state display in the overvoltage protector. The state display indicates whether the overvoltage limiter located in the overvoltage protector is still serviceable or not. Depending on the application of the overvoltage protector, varistors, gas-filled surge arresters, spark gasps or diodes, especially suppressor diodes, are used as overvoltage limiter.
Due to ageing, prior damage by discharge processes and intermittently occurring overvoltages (TOV) in the range of seconds, an unwanted increase of the leakage current of the varistor at operating voltages occurs, especially in overvoltage protectors with a varistor as the overvoltage limiter. Therefore, overvoltage protectors with a varistor as arrester, at present, often have a thermal disconnect device by which a varistor which is no longer reliably serviceable is electrically disconnected from the current path which is to be monitored. Moreover, thermal disconnection devices are often also used in overvoltage protectors with spark gaps as arresters.
Such an overvoltage protector is known, for example, from German Patent Application DE 20 2004 006 227 U1. In the known overvoltage protector, the state of the overvoltage limiter, especially a varistor, is monitored according to the principle of a temperature switch so that, when the varistor overheats, a solder connection provided between the varistor and a disconnector is interrupted; this leads to electrical disconnection of the varistor. Moreover, when the solder connection is interrupted a plastic element is pushed by the reset force of a spring out of a first position into a second position in which the disconnector, which is made as an elastic metal tongue, is thermally and electrically disconnected from the varistor by the plastic element. Since the plastic element has two colored markings which are located next to one another, it also acts in addition as an optical state display, as a result of which the state of the overvoltage protector can be easily read off directly on site. However only one defect of the overvoltage protector can be signaled by such an integrated display.
Since overvoltage protection devices are exposed to high peak current loads, the individual overvoltage limiters can be damaged depending on the level and frequency of the stresses so that the serviceability of the overvoltage elements should generally be monitored. To monitor the serviceability of plug-in overvoltage protectors, Phoenix Contact GmbH & Co. KG sells a portable arrester test device under the name “CHECKMASTER” (catalog TRABTECH 2007, pages 166 to 173) which has a test receiver into which the protective plug which is to be tested at the time can be plugged. In doing so, the current electrical parameters of the overvoltage limiters are determined and compared to reference values, by measuring the tolerance values highly loaded components being identified as damaged beforehand. The arrester test device thus enables—in addition to the display of a defective overvoltage protector—also a precautionary examination of an overvoltage protector. But the disadvantage is that for this purpose the overvoltage protector must be removed from the bottom part of the device so that a test is not possible during operation.